System for testing line balance



Jame 25, E923. 1,459,770

A. L. JONES SYSTEM FOR TESTING LINE BALANCE Filed NOV. 15 1921 INVENTORq\ 1 4L Jam ATTORNEY Patented June 26, 1923.

ALVA L. JONES, 0F ASBURY PARK, NEW JERSEY, ASSIGNOE TO AMERICANrnnnrnonn AND TELEGRAPH COMPANY, A CORPORATION OF NEVJ YORK.

SYSTEM FOR TESTING LINE BALANCE.

Application filed November 15, 1921. 'Serial No. 515,369.

To all whom it may concern:

Be it known that I, ALVA L. Jones, residing at Asbury Park, in thecounty of Monmouth and State of New Jersey, have invented certainImprovements in Systems for Testing Line Balance, of which the followingis a specification.

The principal object of my invention is to provide a new and improvedmethod for testing the balance between a transmission line and itsnetwork. Another object of my invention is to provide suitable apparatuswith which to practice this method. In a more specific aspect myinvention relates to testing the balance between a twowire line and itsnetwork, at the transformer making connection with a four-wire line. Allthese and other objects of my inven 'tion will be illustrated by aspecificexample of procedure thereunder which I shall now describe insome detail with the understanding that the scope of the invention is defined in the appended claims.

An ordinary two-wire transmission line or metallic circuit is indicatedby L in the accompanying drawing, and a four-wire transmission line isshown at L L In the four-wire line, one pair of wires forms a circuitfor transmission in one direction and the other pair of wires forms acircuit for transmission in the opposite direction. L and L are two suchpairs, making the fourwire line. Repeating element-s A and A areinterposed at suitable intervals, amplifying the currents in oppositedirections as indicated by the arrows. v p

A four-wire line may be especially use ful in a cable, whereas atwo-wire line may be suitable foran open wire pole line. The drawing hasrelation to a station where voice currents pass either way between a twowire line L and a four-wire line L, L

The network N balances the line L across the three-winding transformer7H, whose output is connected by a potentiometer P to the input of theamplifier or repeating element A from which the output current goes overthe line L and becoming attenuated at a certain distance, is amplifiedby the repeating element A and so on.

Voice currents coming in the opposite 'direction along the line L passto the potentiometer P then to the amplifier orrepeat ing element Awhose output goes to the points of the three-winding transformerHHowever slight this across which the line L, and its network N arebalanced.

line L and its network N.

the diagram that by shifting both switches S and S up, the output of theamplifier A becomes connected directly to the input ofv the amplifierA,. It will be inevitable that some electrical disturbance will existsomewhere in the sys tem, and therefore there will be a current put fromthe line L into the amplifier A may be, it will be amplified at A andagain at A but if the line L and the network N were in perfect bal- Itwill be seen from output of the element A would get across to the inputof the element A Since the balance cannot be ideally perfect some ofthat amplified energy will get across and be amplified again by theelements A and A in tandem. If the combined gains of the amplifiers A,and A are smaller than the losses in the other parts of the circuit,this energy will be dissipated but if the gains are greater than thelosses, the energy will be increased until limited by the power capacityof the amplifiers.

The high impedance monitoring coil T is bridged across the conductorsbetween the switches S and S and associated therewith is a receiver R. Alow-pass filter F is interposed in these conductors for a purpose whichwill be explained presently. If the circulation of energy through theamplifiers A and A, in tandem builds up suificiently it will beperceived as singing in the receiver R. e

The two amplifiers A and A can be adjusted for gain by means of thepotentiometers P and P and adjustments will be made to the point atwhich singing barely begins. Let the gain in standard miles in amplifierA be at, and in amplifier A9 let it be a It will now be shown that the,

.80 ance none of the amplified energy from the singing point may beexpressed in standard miles by the formula This means that the net gainaround the circuit of A and A is equal to the sum of the gains of thetwo amplifiers less seven miles, which is approximately what is lostacross the three-winding transformer II. The dethe output of sign of thesystem is such that the energy which comes'in over the line Lpractically divides equally to the circuit ot'the .poten-- tiometer Pito the output of the amplifi er A Again the energy which comes from heamplifier A, practically d1- vi des equally between the line L and itsnetwork N. Thus, the net effect of the transformer is to quarter theenergy on each trip around the circuit oi the amplifiers A and A, intandem. Reference to table of standard miles shows that quartering theenergy means a loss of about 6!; standardmiles'. There is a littlefurther inevitable loss in the transformer H so that the figure is takenat 7, instead of 61;.

; By shitting the switch S down so that its blades make contact with thestuds 2 and 3 instead ot l and 2 the connection between the amplifiersA, and A is reversed or transposed, thus reversing the polarity of theidisturhance at this point. One of these conditions will be morefavorable to singing will result in a lower value for the singpoint thanthe other. The lower value isthe true measure of the unbalance.

Usually the balance between the line L and the network M becomes poor atfrequencies outside the useful telephonic range. In case the lines L andare loaded the behavior of he system will not be adversely afiected bythe poor balance, for they will not transmit suchfrequencies; but whenthe am, 'lifiers l l andli are connected directly by the operationot theswitches S and S,, the singing of the system will be determined by thepoor balance at high frequency rather than by the unbalance in theuseful range. To avoid this error, the low pass filter F is included inthe connection. It is so designed asto prevent the transmission offrequencies beyond the useful range, so that the results of the testwill depend only upon conditions which aiiect the operation of thetour-wire circuit.

The singing point will be determined initially in the manner described,and thereafter at intervals in practice, it will be redetermined in thesame manner and if it is less than on the eariler occasion the attendantwill know that the line L and the network N are out of balance to adegree, as compared with their earlier condition. Accordingly, steps maybe taken to rectify the irregularity on the line L that has produced theunbalance, or steps may be taken to adjust the network N so as moreaccurately to balance the line L It will be seen that my method of testutilizes the repeater elements that are in normal service on thetour-wire line and that very little extra apparatus is employed.

Iclaim:

1. The method of measuring unbalance between a two-wire line and itsnetwork at the junction with a four-wire line having re peater elementstherein, which consists in disconnecting said repeater elements on theirsides away from the two-wire line and connecting them in tandem, andadjusting their gain to the singing point.

2. In a transmission system comprising a two-wire line connected.through a threewinding transformer to a tour-wire line having repeaterelements therein, the method of testing unbalance between the two-wireline and its network which consists in disconnecting said repeater onthe side away from the two-wire line and connecting its elements intandem, and adjusting their gain to the singing point. I

3. In a transmission system comprising a two-wire line connected througha threewinding transformer to a tour-wire line having repeater elementstherein, the method of testing unbalance between the two-wire lineaudits network which consists in disconnecting said repeater on the sideaway from the two-wire line and connecting its elements together with alow pass filter all in tandem, and adjnsting their gain to the s ngingpoint.

il In a transmission system comprising a two-wire line connected througha three- W ndi g t an for 9 a ewi e ne having repeater elements therein,the method of t ting nbal n e b twe n t e t line and its network whichconsists in disn c i g sa epe er be the s de my from the two-wire lineand connecting its elements in tandem, adj usting their gain to thesinging point, and taking the sum of the gains in the two repeaters,less the loss at the three-winding transformer, as the gn an singi g Poga 5. In combination, atwo-wire line, a fourwire line, a networksimulating the twowire line, a three-winding transformer interposedbetween the two-wireline and its network and operatively connecting thetwowire line and the tour-wire line, two opposlte repeating elements inthe respective pairs of tllGfOLlPWiIG line, means to disconnect them onthe side away from the. two-wire line, to reconnect them in tandam, andmeans to adjust said elements to determine the gain at'the singingpoint.

6. In combination, a two-wire line, a fourwire line, a networksimulating the twowire line, a three-winding transiormer interposedbetween the two-wire line and its network and operatively connecting thetwowire line and the four-wire line, two opp0- site repeating elementsin the respective pairs of the four-wire line, means to disconnect themon the side away from the two-wire line, to reconnect them in tandem,means to reverse the polarity of this connection, and means to adjustsaid elements to determine the gain at the singing point.

7. In combination, a two-wire line, a four wire line, a networksimulating the twowire line, a three-winding transformer interposedbetween the two-wire line and its network and operatively connecting thetwowire line and the four-wire line, two opposite repeating elements inthe respective pairs of the four-wire line, means to disconnect them onthe side away from the two-wire line, to reconnect them in tandem, meansto suppress currents of frequencies higher than the useful voice range,and means to adjust said elements to determine the gain at the singingpoint. f

8. In combination, a two-wire line, a fourwire line, a networksimulating the twowire line, a three-winding transformer interposedbetween the two-wire line and its network and operatively connecting thetwo- Wire line and the four-wire line, two opposite repeating elementsin the respective pairs of the four-wire line, means to disconnect themon the side away from the two-Wire line, to reconnect them in tandem,means to reverse the polarity of this connection, means to suppresscurrents of frequencies higher than the useful voice range, and means toadjust said elements to determine the gain at the singing point.

9. In combination, a two-wire line, a fourwire line, a networksimulating the twowire line, a threewindiug transformer interposedbetween the two-wire line and its network and operatively connecting thetwowire line and the four-wire line, two opposite repeating elements inthe respective pairs of the four-wire line, switching means todisconnect the repeating elements on the side away from the two-wireline, to reconnect them in tandem, a high impedance receivlng set acrossthe connection made in this way between the two repeaters, and

means to adjust the repeating elements to determinethe gain at thesinging point as observed with the receiving set.

10. In combination, a two-wire line, a four-wire line, a networksimulating the two-wire line, a three-winding transformer interposedbetween the two-wire line and its network and operatively connecting thetw0-wire line and the four-wire line, two- ALVA L. JONES.

